Standard specification and details
Page 12 – Dressing, grading, holing and preparation
Standard Specification for Roof Slating - Dressing, Grading, Holing and Preparation
Dressing, Grading and Holing Slates
Each slate should be inspected and the thicker end selected for the tail. Slates may be holed wither by hand or machine, front the bed towards the face, thus leaving a small counter-sunk hole which takes the fixing nail head. When holing by hand, the slate must be laid flat over a narrow iron with the hole being formed as close to the iron as possible and on the same side as the slate head. Care must be taken to avoid undue spalling. Each slate should be twice nailed at a distance from the tail equal to the holing gauge; each hole being formed as near the edge as practicable (usually between 20 and 25mm). Whilst holing, the slates should be graded according to thickness in three separate parcels. Thicker slates are used on the bottom section of the roof, medium slates in the middle and the thin slates at the top. Any broken slates should be saved and dressed (cut) for under eaves, top slates, half slates or raking cuts. Holing at the head of the slate is not recommended.
Preparation Before Slating
Slating can be either laid direct to softwood batten or boards. In either case an underlay is recommended, either between the battens and rafters or direct to boards. Where battens are laid to boards, it is advisable to lay counter-battens or laths down the roof slope to raise the level, and thus give any moisture that may accumulate a free run down the roof slope. Battens should be laid horizontally across the roof at a vertical distance equal to the battening gauge from the bottom of each batten. The battens should be nailed at not more than 600mm centres, and the ends of each length should always be fully supported.
Underlay over counter-battens on boards
Underlay over open rafters